1. Field of the Invention
The present invention relates to a magnetic head for a magnetic recording/reproduction apparatus and a magnetic recording/reproduction apparatus, and more specifically to a recording head, a combined head and a magnetic recording/reproduction apparatus in which a fluctuation in reproduction characteristics is suppressed even in the case where a material having great saturation magnetization which realizes high recording ability is used for a magnetic core.
2. Description of the Related Art
In accordance with a trend of minimization and enlarging capacity of a magnetic memory device, a volume of per one bit to be recorded on a magnetic medium becomes smaller quickly.
A magnetoresistive effect type head (hereinafter, “MR head”) can detect a magnetic signal generated from this minute bit as a large reproduction output.
This MR head is discussed as “A Magnetoresistivity Readout Transducer” in “IEEETrans. on Magn,. MAG7 (1971) 150”.
Recently, a great magnetoresistive (hereinafter, “GMR”) head using GMR which can realize greatly high output for the MR head has been put into practical use.
In this GMR effect, particularly a magnetoresistive effect which is generally called as a spin-valve effect, in-which a change in resistance corresponds to cosine between magnetization directions of two adjacent magnetic layers, shows a great change in resistance in a weak operating magnetic field. For this reason, the GMR head using this effect is a generic name of “GMR head”.
This GMR head using the spin-valve effect is discussed as “Design, Fabrication & Testing of Spin-Valve Read Heads for High Density Recording” in “IEEE Trans. on Magn,. Vol. 30, No. 6 (1994)3801”.
As for the above GMR head, one magnetic layer of two magnetic layers for producing the spin-valve effect has a magnetization fixed layer where magnetization is fixed so as to be substantially aligned with a direction along which a magnetic field of a medium entering into a head magnetic sensing portion by an exchange coupling magnetic field which is generated by laminating an antiferromagnetic film on the one magnetic layer.
The other magnetic film, which is adjacent to the magnetization fixed layer via a conductive layer made of Cu or the like, is a magnetization free layer in which the magnetization direction can be changed freely with respect to the magnetic filed of the medium. Hereinafter, the GMR head using the spin-valve effect is called as “GMR head”.
FIGS. 6 and 7 are structural diagrams showing concrete examples of a conventional combined head 50 which is composed of a GMR reproduction head 70 and an ID recording head 60. FIG. 7 is a diagram of the structure of the GMR head viewed from an air bearing surface (ABS surface) which is a surface opposed to the magnetic medium. FIG. 6 is a cross section taken along a line A–B of FIG. 7.
Namely, a magnetic separation layer 3 made of an insulating material intervenes between a lower shield 2 and an upper shield 6 which are laminated on a ceramic 1 to be used as a slider, and a spin-valve laminated structure for producing the GMR effect is arranged as a center area 4. An end portion area 5 for supplying an electric current and a bias magnetic field is formed at both the ends of the center area 4. These are GMR elements for reproduction.
Further, the upper shield is used as a first magnetic core 6, and a second magnetic core 11 is arranged on a surface of the magnetic core 6 which is opposite to the GMR elements via a recording gap 7.
Coils 9, which are sandwiched between the recording gap film 7, a non-magnetic insulating material 10a and a non-magnetic insulating material 10b, are arranged in slightly inner portions of the magnetic cores 6 and 11 from ABS.
Recording is carried out by magnetic flux which leaks from the recording gap 7 between the magnetic cores 6 and 11 magnetized by magnetic fields generated from the coils.
The above combined-structure head, in which the GMR or MR reproduction head and the inductive (hereinafter “ID”) recording head are stacked to each other, is called as a combined head here.
A recording density which is actually used by the combined head using GMR has a high-density recording area of not less than 3 GB per inch. A conventional combined head using a material having magnetic anisotropy is sufficient for recording density less than the above density.
Namely, the practical combined head using GMR realizes magnetic recording/reproduction with high density of not less than 3 GB per 1 square inch.
In the reverse way, a magnetic recording/reproduction apparatus which is structured by using the combined head of GMR is an apparatus for carrying out recording/reproduction with high density of 3 GB per 1 square inch.
An ID head which takes responsibility for recording onto a magnetic medium is always required for improvement of a high-density recording. Particularly, a high coercive force of a magnetic medium is essential for high-density recording.
This is because a magnetization transition length to be recorded on a medium is made to be shorter in accordance with the improvement of the recording density, or the magnetization is kept constant even if a magnetization length for 1 bit becomes shorter.
For this reason, a technique for increasing a recording magnetic field has been conventionally developed energetically so that recording can be carried out onto high coercive force medium as an ID head which is suitable for high-density recording.
Conventionally, an Ni—Fe plated film (hereinafter, permalloy) in which Ni is about 80 weight % has been used as a magnetic core of the ID head. This material has saturation magnetization (Bs) of about 1 T (tesla), and recording of 3 GB per 1 square inch can be carried out. This is described in “3 Gb/in2 recording demonstration with dual element heads & thin film disks” of “IEEE Trans. on Magn,. Vol. 32, No. 1 (1996) pp. 7–12”.
However, in order to carry out recording of not less than 5 GB per 1 square inch, an Ni—Fe plated film in which Ni is about 45 weight % (hereinafter, 45NiFe) is required instead of the permalloy. This is described in “5 Gb/in2 recording demonstration with conventional ARM dual element heads & thin film disks” of “IEEEE Trans. on Magn,. Vol. 33, No. 5 (1997) pp. 2866–2871”.
This material has saturation magnetization of about 1.6 T (tesla) maximally. Moreover, with this material, recording of about 12 GB per 1 square inch can be carried out. This is described in “12 Gb/in2 recording demonstration with SV read heads & conventional narrow pole-tipwrite”of “IEEE Trans. on Magn,. Vol. 32, No. 1 (1996) pp. 7–12”.
Meanwhile, examples using an Ni—Fe plated film in which Bs is about 1.6 are disclosed in the Japanese Unexamined Patent Publication (KOKAI) Nos. 8-212512 (1996) and 11-16120 (1999).
In addition, an example using a high saturation magnetization Bs material formed by a sputtering method is disclosed in the Japanese Unexamined Patent Publication (KOKAI) No. 10-162322 (1998), and in this example, a Co amorphous film represented by a Co—Ta—Zr sputtering film is used.
The Co amorphous film can have high Bs up to about 1.5 T. Moreover, the Japanese Unexamined Patent Publication (KOKAI) No. 7-262519 (1995) discloses an application of high Bs materials such as ferric nitride. It is considered that an iron-nitrogen material can have high Bs of about 1.9 T.
Further, in the case where simplicity and cost reduction of a manufacturing process for a magnetic head are considered, it is effective to form a magnetic material forming a recording magnetic pole according to a z plating method.
In the plating method, a photoresist frame through which a form of a magnetic pole previously pierces is formed, and a plated film is allowed to grow in the frame so that a desired pattern can be obtained. Because of the simplicity and cost reduction of this method, this method is currently a standard manufacturing method of a thin film magnetic head.
Meanwhile, in the case where a magnetic core pattern is formed by the sputtering method, a photoresist mask is formed on a magnetic film previously formed into a core shape, and the core pattern is formed by etching using an ion beam.
In this method, first, an expensive ion beam etching apparatus is required, and second, a long processing time is required for patterning a thick magnetic core film of several μm, and third, it is very difficult to form magnetic core end portions with narrow width which determine a recording width on a medium.
Particularly, as shown in FIG. 6, it is very difficult to pattern the upper core 11 under a condition that there exists a great level difference between the coils and their upper and lower insulating layers.
The Japanese Unexamined Patent Publication (KOKAI) No. 7-262519 (1995) discloses a method of forming only magnetic core end portions before forming a great level difference between coils and insulating layers and introducing an ion-nitrogen sputtering film into the magnetic core end portions. However, this is originally a method using ion beam etching and is not a low-priced manufacturing method.
As mentioned above, when the sputtering film is applied to the magnetic core, a rise of the cost due to complication of the manufacturing method is inevitable.
In addition, in accordance with improvement of the recording density, it is considered that a high Bs film with more than 1.5 T obtained by 45Ni—Fe is indispensable. It is very important to realize the high Bs film according to the low-priced plating method. Co—Fe—Ni is promising as a material of a plated film which realize high Bs of more than 1.5 T.
Further, in a composition diagram of three elements in FIG. 1 of the Japanese Examined Patent Publication (KOKOKU) No. 63-53277 (1988), a line of magnetostriction λs=0 in a Co—Fe—Ni plated film is shown, and in a composition diagram of three elements in FIG. 2 of this publication, Bs in the Co—Fe—Ni plated film is shown.
According to this diagrams, Bs around 80Co10Fe10Ni where λs become substantially zero is about 1.6 T.
Meanwhile, in the Japanese Unexamined Patent Publication (KOKAI) No. 6 -346202 (1994), crystallizability of the Co—Fe—Ni plated film is adjusted so that both low-magnetostriction and high Bs, which cannot be realized in Japanese Examined Patent Publication (KOKOKU) No. 63-53277 (1988), are compatible with each other.
As a result, a Co—Fe—Ni plated film in which Bs is about 1.7 T when λs<5×10−6, is obtained.
In addition, the Japanese Unexamined Patent Publication (KOKAI) No. 7-3489 (1995) describes that a low coercive force is obtained by adjusting crystallizability and Bs which falls within a range of 1.3 to 2 T is obtained.
Further, in Publication of Japanese Patent No. 2821456, a Co—Ni—Fe plated film is deposited in a bath without an additive containing S such as saccharin, and the high-purity film, in which sulfur concentration in the film is suppressed to not more than 0.1 weight %, is obtained.
As a result, a mixed crystal composition of fcc and bcc transfers to an area with many Fe compositions, and the magnetostriction is lowered to a practical level in this composition, and extremely high Bs of 1.9 T to 2.2 T as well as satisfactory soft magnetic characteristic in which a coercive force is not more than 2.50 e are realized.
As mentioned above, the Co—Ni—Fe plated film can realize the practical soft magnetic characteristic as a magnetic core material of ID head by controlling crystallizability and content of mixture into the film. As disclosed in Patent No. 2821456, Bs can be extremely large and satisfactory soft magnetic can be realized.
As mentioned above, the Co—Ni—Fe film or 45NiFe film, which is formed by the plating method and has great saturation magnetization, is very preferable for a recording core material for achieving high-density magnetic recording. However, since these films have the following properties, there have conventionally arose various problems due to these properties.
Namely, the first problem is that the magnetostriction of the Co—Ni—Fe film or 45NiFe film with high Bs is positive.
For example, in the case where the 45Ni—Fe film is applied to an upper shield of a GMR reproduction head which also serves as a recording core, a fluctuation in a reproduced output after recording operation is very conspicuous, and thus it becomes a combined head which cannot be practically used.
This is because as the magnetostriction is positive, a magnetization state of the upper shield after recording operation is hardly stabilized, and a reproduction characteristic is adversely affected therefrom.
Therefore, the 45NiFe cannot be applied to the upper shield which also serves as the magnetic core for recording.
For this reason, the 45NiFe with great saturation magnetization can be applied only to the upper core, and since normal permalloy is applied to the upper shield, the recording ability itself is limited.
In addition, as for the Co—Ni—Fe film, its magnetostriction is controlled so as to be changed from positive to negative by controlling a composition, but the magnetostriction is positive in the composition where the saturation magnetization is great, namely, not less than 1.7 T. Accordingly, the problem which is the same as that of the 45NiFe arises.
Further, in the case of the permalloy which has been conventionally used for the upper shields, since the magnetostriction of the permalloy film is controlled by a film composition, it is necessary to strictly control the composition so that the magnetostriction suitable for the upper shield is obtained. This causes a rise of the manufacturing cost.
In addition, the second problem is that a stress is strong particularly in a Co—Ni—Fe film whereby the saturation magnetization is great, namely, about 2 T.
The stress is about 0.8 GPa, and when a thick film of not less than 2 μm is intended to be formed, peeling of the film is conspicuous.
As a result, when the whole upper magnetic core is intended to be formed by a Co—Ni—Fe film which shows great saturation magnetization, the film thickness of not less than 2 μm is required, and thus the manufacturing is difficult.
As a method of applying the Co—Ni—Fe film to the upper magnetic core, a method of forming a Co—Ni—Fe film having a thickness of 0.5 μm in a vicinity of a recording gap and laminating a permalloy having a thickness of about 3.5 μm has been used.
Also with this method, the effect of the material with high saturation magnetization is successfully brought out, but in order to bring out the effect maximally it is desirable to form the whole core using a Co—Ni—Fe film.
Further, the third problem is that as the recording density is improved, the recording head requires an operation with higher frequency. Particularly in a Co—Ni—Fe film where saturation magnetization is large, namely, about 2 T, since a specific resistance is small, namely, about 20μΩcm, an overcurrent loss in high-frequency operation increases, and the recording characteristic is easily deteriorated.